9.

Catfish can grow to considerable size. To accelerate their growth, many fish farmers feed them hormones, especially those fish imported from Asian countries. Free-grown catfish are much less dangerous and more nutritionally valuable.

8.

Mackerel contains mercury, which is not cleared from but accumulated in the human body, causing various diseases. The Atlantic mackerel is the least dangerous in this regard, and you can eat it as much as you like.